Solve for x: log₈ x + log₄ x + log₂ x = 11. Use base conversion (let y = log₂ x) to reduce to a linear equation.

Difficulty: Medium

Correct Answer: 64

Explanation:


Introduction / Context:
The equation mixes logarithms with bases 8, 4, and 2 applied to the same x. Converting all to base 2 simplifies the problem to a single-variable linear equation.


Given Data / Assumptions:

  • log₈ x + log₄ x + log₂ x = 11
  • x > 0


Concept / Approach:
Let y = log₂ x, so x = 2^y. Then log₄ x = y/2 (since 4 = 2^2) and log₈ x = y/3 (since 8 = 2^3). Substitute and solve for y, then recover x = 2^y.


Step-by-Step Solution:

Let y = log₂ xThen log₄ x = y/2 and log₈ x = y/3Sum: y/3 + y/2 + y = 11 ⇒ (2y + 3y + 6y)/6 = 11 ⇒ 11y/6 = 11 ⇒ y = 6Therefore x = 2^6 = 64


Verification / Alternative check:
Compute each term: log₂ 64 = 6, log₄ 64 = 3, log₈ 64 = 2; sum 6 + 3 + 2 = 11, confirming the solution.


Why Other Options Are Wrong:
2, 4, and 8 yield sums far smaller than 11; only 64 produces the required sum.


Common Pitfalls:
Forgetting the base-change scaling (dividing by 2 or 3) or mis-adding fractions can produce a wrong y value. Carefully use common denominators.


Final Answer:
64

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